1. Field of the Invention
The present invention relates generally to a power control apparatus and method in a mobile communication system. In particular, the present invention relates to a power control apparatus and method for transmitting control information using a pilot pattern in a mobile communication system.
2. Description of the Related Art
Code Division Multiple Access (CDMA) mobile communication systems have been developing from an IS-95 standard for mainly supporting transmission/reception of voice signals into an IMT-2000 standard capable of supporting not only the voice signal transmission but also high-speed data transmission. The IMT-2000 standard aims at providing high-quality voice service, moving image service, Internet search service, and the like.
In the mobile communication system, various schemes for servicing such information as voice and data are being realized. A conventional scheme is a High Speed Downlink Packet Access (HSDPA) scheme in a Universal Mobile Telecommunications System (UMTS) communication system.
Generally, the HSDPA scheme refers to a data transmission scheme, including a high speed-downlink shared channel (HS-DSCH), which a downlink data channel for supporting high-speed downlink packet data transmission, and its associated control channels. In order to support the high-speed downlink packet data service, an Adaptive Modulation and Coding (AMC) scheme, a Hybrid Automatic Retransmission Request (HARQ) scheme, and a Fast Cell Select (FCS) scheme have been proposed. A description will now be made of the HARQ scheme, especially, an n-channel Stop And Wait HARQ (n-channel SAW HARQ) scheme.
In the HARQ scheme, the following two counterplans have recently been applied to increase transmission efficiency of an Automatic Retransmission Request (ARQ) scheme. According to a first counterplan, retransmission request and Acknowledgement/Negative-Acknowledgement (ACK/NACK) are exchanged between a user equipment (UE) and a Node B. According to a second counterplan, a UE temporarily stores defective data and combines the stored defective data with retransmitted data of the corresponding defective data before decoding. The high-speed downlink packet data service method has introduced the n-channel SAW HARQ scheme in order to compensate for the defect of the conventional Stop and Wait ARQ (SAW ARQ) scheme. In the case of the SAW ARQ scheme, next packet data cannot be transmitted before an ACK for previous packet data is received. Therefore, in some cases, a UE needs to wait for an ACK even though it can currently transmit packet data.
In the n-channel SAW HARQ scheme, a UE continuously transmits a plurality of data packets before it receives the ACK for a previous data packet, thereby increasing channel efficiency. That is, if each of n logical channels established between a UE and a Node B can be identified by a specific time or its unique channel number, the UE receiving packet data at a specific time can determine a channel over which the packet data was received. Therefore, the UE can take necessary measures such as an operation of reordering data packets in their right reception order and an operation of soft-combining the corresponding data packets.
Table 1 and Table 2 below illustrate downlink and uplink physical channels used in a mobile communication system, respectively.
TABLE 1DownlinkPhysical ChannelsFunctionsDPDCHDedicated Physical Data ChannelDPCCHDedicated Physical Control ChannelCPICHCommon Pilot ChannelP-CCPCHPrimary Common Control Physical ChannelS-CCPCHSecondary Common Control Physical ChannelSCHSynchronization ChannelPDSCHPhysical Downlink Shared ChannelAICHAcquisition Indicator ChannelAP-AICHAccess Preamble Acquisition Indicator ChannelPICHPaging Indicator ChannelCSICHCPCH (Common Packet Channel) Status IndicatorChannelCD/CA-ICHCPCH Collision Detection/Channel AssignmentIndicator ChannelHS-PDSCHHigh Speed-Physical Downlink Shared ControlChannelHS-SCCHHigh Speed-Shared Control Channel
TABLE 2Uplink Physical ChannelsFunctionsDPDCHDedicated Physical Data ChannelDPCCHDedicated Physical Control ChannelPRACHPhysical Random Access ChannelPCPCHPhysical Common Packet ChannelHS-DPCCHHigh Speed-Dedicated Physical ControlChannel
The downlink physical channels are distinguished using orthogonal variable spreading factor (OVSF) codes.
In order to support a packet data service with an uplink in a mobile communication system, a similar scheme to the scheme for supporting a packet data service with a downlink can be introduced. Therefore, in order to constitute a packet data service in an uplink, it is necessary to transmit packet data of the uplink and control information of the downlink. The control information refers to, for example, “ACK/NACK information.” A scheme for transmitting control information including the ACK/NACK information using the downlink is classified into a scheme for transmitting the control information over an existing physical channel after time multiplexing, and a scheme for transmitting the control information over the existing physical channel after code multiplexing.
The time multiplexing scheme and the code multiplexing scheme will be described herein below with reference to FIGS. 1 and 2, respectively.
FIG. 1 illustrates a structure of a downlink physical channel for time-multiplexing control information for packet data transmission with data before transmission. The types and functions of physical channels in the downlink have been illustrated in Table 1. Referring to FIG. 1, the control information is time-multiplexed to a space generated by puncturing data on a physical channel, before being transmitted. That is, the physical channel includes the control information in a partial duration where no data is transmitted, before being transmitted.
FIG. 2 illustrates a structure of a downlink physical channel for code-multiplexing control information for packet data transmission with an existing physical channel before transmission. Referring to FIG. 2, a separate physical channel for transmitting control information is generated in addition to an existing physical channel, and the control information or packet data is transmitted over the generated physical channel. The existing physical channel and a physical channel recently defined for transmitting the control information are separated using OVSF codes. Also, the physical channel for transmitting the control information can include control information indicating an information transmission channel.
The time multiplexing scheme illustrated in FIG. 1 should include control information for packet data transmission in a partial duration of an existing physical channel, causing a possible loss of data transmitted over the existing physical channel. Although the code multiplexing scheme illustrated in FIG. 2 prevents a data loss in the existing physical channel, it needs additional power and OVSF code for the physical channel generated to transmit the control information.
Therefore, the present invention proposes a scheme for transmitting control information using the existing physical channel. Some types of control information for packet data transmission do not have a large amount of information, so that they can be transmitted through a modification of the existing physical channel. Such a method does not need additional codes and power for transmitting control information, and minimizes the influence on performance of the existing physical channel. For example, in an asynchronous mobile communication system, the method can transmit control information using a pilot duration existing in a physical channel. A dedicated physical control channel (DPCCH) can be used as the physical channel.
However, in the forgoing scheme using a pilot duration, if the pilot duration is not long enough, an error rate will probably increase when a reception side extracts control information. Because the occurrence of an error causes mis-operations, it is necessary to reduce the error rate.